PTP1C belongs to a family called SH2-PTP, which are protein tyrosine phosphatases containing two SH2 domains at their N-terminals. PTP1C behaves as the negative regulator involved in the differentiation of hematopoietic cells. It is also the tumor suppressor gene involved in leukemia, ovary cancer and other cancers. In this proposal, we are applying for the synchrotron time to collect a set of high resolution native data, from the crystals of the catalytic domain of PTP1C. The crystals have the sizes of 0.1 x 0.1 x 0.1 mm3. It diffracts to 3.0 at -160oC, using the RAXIS-II machine at the UMASS Medical Center. The space group is C222, with two molecules in the asymmetric unit. The unit cell dimensions are a= 117.048 , b= 132.649 , c= 134.989 . However, the Rmerge of the diffraction data is 15%. Therefore, we are applying for the synchrotron time to collect a set of high resolution native data at CHESS. We intend to solve the structure with the molecular replacement method, by using the crystal structure of PTP1B as the search model. The sequence identity between PTP1B and PTP1C is 35%. If necessary, we will screen the heavy atom derivatives using the RAXIS machine at the UMASS Medical Center.